It is good to see a discussion on engine lubricants and it being sensible and not a flame war.
I became an AMSOIL dealer in 2000. It is in everything I own and has served me well. I have sent in some UOA's that I thought the oil would have been toast and they came back fine and then some that were not.
It does make a difference in application and driving style. Everyone is different and each brand of lubricant will show different results in each case.
We had a 2008 Acadia with the 3.6. No matter what brand oil I used, it was shot at 5k miles. Each UOA came back with the same result. Now we have a 2011 Acadia and this engine is a little better on the oil but I still can't go past 5k. It isn't as hard on the oil but the high fuel dilution is one of the major factors on the oil taking a hit. What is interesting is the 2011 is direct injected and the 08 was not, but they both had high fuel dilutions.
I have noticed that the transmission temp runs cooler since I switched it over to AMSOIL's Torgue Drive fluid. It use to run at 180 and now runs about two needle thickness below that.